The invention relates generally to wireless communication systems and, more particularly, to rate control in multiple antenna communication systems.
It has been shown that wireless communication systems with multiple antennas can provide significant performance improvements and achievable data rates over single antenna systems, in particular in fading environments. The time varying nature of the channel quality in wireless environments (referred to as “fading”) causes random fluctuations in the received power level and, as a result, can lower the probability of reliable decoding. The attempted transmission rate may exceed the instantaneous channel capacity, a phenomena know as outage. Much effort has been directed recently to minimizing the outage probability through various adaptive transmission schemes.
The performance gains provided by multiple antennas systems can be considerably higher if knowledge of the channel state information is available. Unfortunately, in practical systems, it is often only possible to obtain an estimate of the channel state information at the receiver. Moreover, the receiver is usually limited to using a feedback link with a very limited capacity (e.g., a few bits of feedback per block of transmission) when providing the channel state information to the transmitter.